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Comparability of Electroultrafiltration and Ammonium Acetate-LactateExtraction Data for Phosphorus and Potassium in Pseudogley SoilsTihana Tekli a; Vladimir Vukadinovi a; Blaženka Berti a; Zdenko Lonari a

a Department of Agroecology, Faculty of Agriculture, University of J. J. Strossmayer, Osijek, Croatia

Online Publication Date: 01 January 2009

To cite this Article Tekli, Tihana, Vukadinovi, Vladimir, Berti, Blaženka and Lonari, Zdenko(2009)'Comparability of Electroultrafiltrationand Ammonium Acetate-Lactate Extraction Data for Phosphorus and Potassium in Pseudogley Soils',Communications in Soil Scienceand Plant Analysis,40:1,599 — 609

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Comparability of Electroultrafiltration andAmmonium Acetate–Lactate Extraction Data for

Phosphorus and Potassium in Pseudogley Soils

Tihana Teklic, Vladimir Vukadinovic, Blazenka Bertic, and Zdenko

Loncaric

Department of Agroecology, Faculty of Agriculture, University of J. J.

Strossmayer, Osijek, Croatia

Abstract: The aim of this research was to compare two standardized soil

extraction methods [electroultrafiltration (EUF) and ammonium acetate–lactate

(AL)] regarding potassium (K) and phosphorus (P) availability in pseudogley

soils. In total, 60 pseudogley soil samples from 12 agricultural sites in eastern

Croatia (each represented by five soil samples—replicates) were simultaneously

analyzed by both methods. The relations of K and P with other important soil

traits [pH, selective mineral clay content (SMC), humus content] were established

by multiple regression analyses. Furthermore, a highly significant regression

equation (P ( 0.01) was established for AL–phosphorus pentoxide (P2O5), using

EUF-P-I and EUF-P-II separately as well as soil pH value determined in 1 M KCl

as independent variables. The actual P amount extracted by AL differed by 9%

from the value predicted by the regression function. According to the highly

significant multiple regression function (P ( 0.01), AL-extractable dipotassium

oxide (K2O) can be approximated using EUF-K (sum of EUF-K-I and EUF-K-II

fraction), SMC, and the EUF-K-Q (ratio of EUF-K-II and EUF-K-I) as the

independent variables. A deviation of calculated AL-K2O value from the

extracted amount of K was 4%. These results point out the possibility of the

comparison of EUF and AL extraction data in the evaluation of K and P

availability in pseudogley soils. The necessity of more comprehensive research

regarding the comparison of the EUF and AL method, taking into account plant

nutrient acquisition specificity and a great number of interrelated soil and climate

factors, was suggested.

Address correspondence to Tihana Teklic, Department of Agroecology,

Faculty of Agriculture in Osijek, University of J. J. Strossmayer, HR-31000

Osijek, Croatia. E-mail: tteklic@pfos.hr

Communications in Soil Science and Plant Analysis, 40: 599–609, 2009

Copyright # Taylor & Francis Group, LLC

ISSN 0010-3624 print/1532-2416 online

DOI: 10.1080/00103620802649252

599

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Keywords: Ammonium acetate–lactate, electroultrafiltration, phosphorus,

potassium

INTRODUCTION

The classical methods of single extraction of plant nutrients from soils are

common in agriculture with the aim of determining plant fertilizationrequirements. However, these methods, although widely accepted and

applied, do not give all necessary information regarding nutrient

availability to plants. Additional soil analysis such as organic-matter

content, pH value, texture, and cation exchange capacity of the soil

should be performed occasionally. Electroultrafiltration (EUF) combines

electric field, ultrafiltration, and temperature to extract cations and

anions from soil with water, usually collected in two fractions. The first

fraction, representing readily available nutrients, is obtained at 200 V, 20uC, and 15 mA during the first 30 min. The second fraction, considered as

spare nutrients, is obtained in the next 5 min by applying 400 V, 80 uC,

and 150 mA. As an addition to this standard procedure, there is the

possibility of introducing a well-known complexing, agent diethylene-

triaminepentaacetic acid (DTPA), in the third EUF fraction (5 min at 80

uC), which enables better extraction of micronutrients and trace elements,

as reported by Horn (2006).

It is desirable that a soil-extraction method determine the soil bufferpower for nutrients (Vukadinovic et al. 2003). The major advantage of

the EUF method in comparison with other chemical extraction methods

is obtaining information on many plant nutrients and their chemical

potential in the soil with use of one soil sample and a single (commonly

two-phase) extraction. The comparison of the EUF method with other

analytical methods was intensive, considering soil nitrogen (N), especially

related to the Nmin method (Heyn and Brune 1989; Mengel 1991) and

calcium chloride (CaCl2) extraction (Mengel, Schneider, and Kosegarten1999; Dou, Alva, and Appel 2000; Matsumoto and Ae 2004; Dıez and

Vallejo 2005). Regarding the methods for the evaluation of phosphorus

(P) and potassium (K) availability, there is a large number of reports

dealing with various extractants and methods (Indiati and Singh 2001;

Sardi and Fuleky 2002; Sonar and Palwe 2002; Zbiral and Nemec 2002),

including EUF (Houba et al. 1986; Rao et al. 2000; Ziadi et al. 2001a,

2001b; Akinrinde, Obigbesan, and Gaiser 2006; Fuleky, Tolner, and

Anas 2006). However, ammonium acetate–lactate extraction (ALmethod), which is the official extraction method for P and K in

Croatia, was rarely compared to EUF, as stated by Hahlin (1982).

Pseudogley is a common name in many national soil classification

systems for most stagnosols, characterized by a perched water table and

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showing redoximorphic features caused by surface water. These soils

are periodically wet and mottled in the topsoil and subsoil, with or

without concretions and/or bleaching. The soil factors influencing P

and K availability in the soil such as pH and clay content are important

parameters of fertility potential of pseudogley and similar soils. These

factors can greatly influence P and K extraction and comparison of

different analytical methods, as reported by Loncaric et al. (2006). The

aim of the research presented here was to evaluate the comparison of

AL and EUF methods regarding P and K extraction from pseudogley

soils.

MATERIALS AND METHODS

Soil samples from the surface layer (0–30 cm deep) were collected from

12 agricultural sites in eastern Croatia with pseudogley soil type, and

each locality was represented by five average soil samples (repetitions).

The soil samples were prepared by drying in a thermostatically

controlled oven at a temperature of 40 uC ¡ 2 uC. The determination

of soil pH was made in 1:5 (v/v) suspensions of soil in a 1 M KCl

solution. Soil organic matter (humus content %) was determined by

sulfochromic oxidation as prescribed by ISO (1998). A correction

factor of 1.724 was used to calculate humus content from the carbon

result.

Ammonium acetate–lactate–phosphorus pentoxide (P2O5) and AL–

dipotassium oxide (K2O) were extracted using AL–acetic acid extractant

described by Egner, Riehm, and Domingo (1960). This procedure, called

also the Egner–Riehm–Domingo method for plant-available P and K,

has been the most commonly used soil P and K test in Croatia for more

than 30 years (Loncaric et al. 2006). The method gives the results in mg of

P2O5 and K2O, respectively, per 100 g of air-dry soil, and here the results

are given in mg kg21 soil. EUF extraction was performed by obtaining

two fractions of P and K expressed in mg per 100 g of dry soil, which were

transformed in mg kg21, and their sum was noted as EUF-P and EUF-K.

The EUF-P-Q and EUF-K-Q are calculated as the ratio of the second

and the first EUF fraction. Phosphorus and K concentration in liquid

extracts from both methods were determined by spectrophotometry and

flame photometry, respectively. Selective mineral clay content (SMC) was

determined using the function based on EUF-K-Q and EUF-K-II, as

reported previously (Teklic et al. 2002).

The results of soil analysis were tested using single correlation and

multiple regression analysis, whereas the significance of the established

regressions showing the relationships among nutrient availability

parameters was tested by F-test and t-test. Functions describing the

EUF and AL extraction of soil P and K 601

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relationships among P and K extractability parameters were calculated

using data obtained by tested analytical methods (usually expressed in mg

per 100 g of dry soil). However, in the comparison of measured nutrient

data and those calculated using the most significant regression functions,

data were expressed in mg kg21 of dry soil.

RESULTS AND DISCUSSION

The selected pseudogley soils had a pH range of 4.05–6.09, humus

content from 1.18 to 1.70% (Table 1), and SMC from 13.38 to 23.78%

(Table 2). The highest concentration of readily extractable P, the first

EUF fraction, was found in samples from locality no. 7, and the greatest

value of less soluble P defined by the second EUF fraction was in locality

no. 12. However, the quotient representing soil P supply potential was the

highest in locality no. 8. Total EUF-extracted P ranged from 10.8 to

21.8 mg kg21, and AL-extracted P ranged between 102.4 and

214.4 mg kg21 of dry soil. The average total extracted EUF-P was 17.1,

and AL-extracted was 153.1 mg kg21 soil (Tables 1 and 2). These values

are in concordance with the statement that the EUF-extracted P amount

represents 10–30% of lactate-extractable P (Nemeth 1988). The most

significant impact on P extractability had soil pH, which was related to

both EUF fractions and AL-extracted P amount by quadratic functions

(Table 3). Both EUF-P fractions were significantly correlated to

Table 1. Analysis of pseudogley soil samples from 12 locations in eastern

Croatia

Locality pH

(1 M KCl)

Humus content

(%)

AL-P2O5

(mg kg21)

AL-K2O

(mg kg21)

1 4.44 1.29 137.6 210.0

2 4.31 1.25 128.0 195.2

3 5.34 1.64 174.4 219.6

4 6.04 1.70 200.0 183.2

5 4.19 1.18 144.8 243.6

6 4.05 1.69 124.0 210.0

7 6.09 1.54 214.4 294.0

8 6.02 1.60 185.6 137.2

9 4.50 1.34 104.8 184.0

10 4.48 1.21 102.4 203.6

11 5.29 1.38 179.6 205.2

12 5.46 1.39 141.2 206.8

Mean 5.02 1.43 153.1 207.7

Note. AL-ammonium acetate-lactate extraction; data are means of five

replications.

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AL-P2O5, with slightly higher determination coefficient for EUF-P-I

(Figure 1). However, the prediction of AL-P from this EUF-P fraction

using the presented mathematical function would not be recommended,

because the importance of other P forms and other soil traits should not be

neglected. Therefore, it was necessary to include more parameters into the

regression model. The best fit with the highest significance was obtained

with the regression function presented in Tables 4 and 5. The Al-P2O5 was

taken as the dependent variable, and both EUF-P fractions as well as pH

were independent variables. Here, EUF-calcium (Ca) fractions were not

significantly correlated to P or K extractability, and therefore are not

shown and are not taken into account in the multiple regression analysis.

According to the F-test and t-test, this regression was significant at P (

0.01. The calculated AL-P2O5 values differed from the actual data

obtained by soil extraction (the regression error or residual output) by 9%.

Accordingly, the conversion of the EUF-extractable P to AL-extractable P

could be done with an error possibility of less than 10%.

The EUF-K fractions and their ratio have importance not only for

soil K evaluation but may also give an insight into soil clay selectivity for

K (SMC), which has a major impact on K plant-availability rate. After

Nemeth (1982), the quantities of K desorbed within 30 min at 20 uC and

200 V generally decrease with increasing K-selective clay minerals in the

soil and with decreasing degree of their saturation with K. As reported by

Rubio and Gil-Sotres (1996), in soils with a predominance of micaceous

Table 2. EUF analyses of pseudogley soil samples from 12 locations in eastern

Croatia

Locality EUF

P-I

EUF

P-II

P-Q EUF-P EUF

K-I

EUF

K-II

K-Q EUF-K SMC

(%)

1 10.4 6.1 0.59 16.5 92.5 27.9 0.30 120.4 14.64

2 10.3 5.4 0.52 15.7 93.8 27.5 0.29 121.3 14.11

3 11.6 7.3 0.63 18.9 112.0 39.4 0.35 151.4 17.15

4 12.8 7.8 0.61 20.6 78.7 35.5 0.45 114.2 19.07

5 9.4 6.3 0.67 15.7 132.2 39.1 0.30 171.3 16.20

6 7.5 4.0 0.53 11.5 111.6 27.5 0.25 139.1 13.38

7 14.2 7.6 0.54 21.8 158.5 45.3 0.29 203.8 16.49

8 11.4 8.1 0.71 19.5 66.5 25.5 0.38 92.0 16.24

9 8.5 2.3 0.27 10.8 78.2 32.1 0.41 110.3 17.67

10 7.7 5.0 0.65 12.7 100.2 30.2 0.30 130.4 14.82

11 13.0 6.6 0.51 19.6 89.7 40.1 0.45 129.8 19.06

12 14.0 8.4 0.60 22.4 121.3 61.7 0.51 183.0 23.78

Mean 10.9 6.2 0.57 17.1 102.9 36.0 0.36 138.9 16.88

Note. P-Q and K-Q ratio of EUF-II and EUF-I fraction; EUF-P, EUF-K sum

of EUF-I and EUF-II fractions; data are means of five replications; nutrient

content expressed in mg kg21 of dry soil.

EUF and AL extraction of soil P and K 603

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minerals in their clay fraction, K added by fertilizers to illitic soils was

mostly in soil solution, whereas that added to vermiculitic soils was

mostly internal, after EUF analyses. In general, tested pseudogley soils in

our research showed medium supply with K, regarding both extraction

methods. The locality with the lowest readily available K defined by

EUF-K-I as well as total K content (EUF-K, Table 2) showed also the

lowest AL-K2O (locality no. 8, Table 1). Locality no. 7 had the highest K

obtained with both applied methods. Almost equal SMC (Table 2) and

high difference in K in the two soils established by both extraction

methods point out the importance of taking into account soil texture for

soil K data evaluation. The SMC was significantly correlated to EUF-K-

II and EUF-K-Q, as expected. EUF-K-I was closely related to AL-K2O

(Figure 2), unlike EUF-K-II. However, EUF-K-II participates in total

EUF extractable potassium (5EUF-K-I + EUF-K-II) and therefore

might have an influence on the significant relationship between EUF-K

and AL-K2O (Table 2). The conversion of EUF-extracted K to an AL-

extractable amount seems possible, using the regression equation presented

in Tables 6 and 7. The best fit was obtained when total EUF-K, K-Q,

Table 3. Correlative relationships among selective mineral clay content (SMC),

pH (in 1 M KCl), and EUF as well as AL-extractable phosphorus and potassium

in tested pseudeogley soils

X Y R2 Function equation

SMC EUF-K-II 0.734 EUF-K-II 5 0.0178 6 (SMC)2 2 0.3512 6SMC + 4.3197

K-Q 0.868 EUF-K-Q 5 20.0011 6 (SMC)2 + 0.0672 6SMC 2 0.456

pH EUF-P-I 0.722 EUF-P-I 5 20.1273 6 (pH)2 + 1.5478 6 pH

2 3.4014

EUF-P-II 0.583 EUF-P-II 5 20.0237 6 (pH)2 + 0.4214 6pH 2 0.8801

AL-P2O5 0.771 AL-P2O5 5 1.9304 6 (pH)2 2 15.619 6 pH

+ 44.019

EUF-P-I EUF-P-II 0.688 EUF-P-II 5 20.5902 6 (EUF-P-I)2 + 1.9179

6 (EUF-P-I) 2 0.7357

AL-P2O5 0.648 AL-P2O5 5 29.567 6 (EUF-P-I)2 + 33.368

6 (EUF-P-I) 2 92.218

EUF-P-II AL-P2O5 0.627 AL-P2O5 5 7.66761.0641 6 (EUF-P-II)

EUF-P AL-P2O5 0.710 AL-P2O5 5 9.7377 6 (EUF-P)0.8303

EUF-K-I AL-K2O 0.869 AL- K2O 5 0.0163 6 (EUF-K-I)2 + 0.9784

6 (EUF-K-I) + 8.8746

EUF-K AL-K2O 0.779 AL- K2O 5 6.8644 6 EUF-K0.6915

Note. EUF, electroultrafiltration method; AL, ammonium acetate–lactate

extraction; K-Q ratio of EUF-K-II and EUF-K-I fraction; EUF-P, EUF-K sum

of EUF-I and EUF-II fractions; n 5 12.

604 T. Teklic et al.

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and SMC were used as independent variables, showing even higher

significance and coefficient of determination in comparison with K

regression. Accordingly, the regression error was lower, and AL-K2O

predicted by this model differed from the real data only 4%. The highest

error was obtained for soil samples from locality no. 8, where the lowest K

content was determined by both methods. Based on these results, the more

comprehensive research regarding the comparison of EUF and AL method

in terms of P and K availability in pseudogley soils is needed that should

take plant specificity in nutrient acquisition and a great number of

interrelated soil and climate factors into account.

Figure 1. Correlation between EUF-extracted phosphorus in the first EUF

fraction (EUF-P-I; mg kg21 of soil dry weight) and ammonium acetate–lactate–

extracted phosphorus (AL-P2O5; mg kg21 of soil dry weight) from pseudogley

soils at 12 localities in eastern Croatia (data points represent means of five

replicates).

Table 4. Multiple regression analyses of the relationships among AL- and

EUF-extractable phosphorus (mg per 100 g dry soil) and pH value in selected

pseudogley soils of eastern Croatia. (** P ( 0.01)

Parameter Standard deviation Variability (%)

EUF-P-I 0.23 21.37

EUF-P-II 0.18 29.17

pHKCl 0.77 15.42

AL-P2O5 3.69 24.13

Regression function: AL-P2O5 5 23.7193 + 2.7366 6 EUF-P-I + 3.7913 6EUF-P-II + 2.7258 6 pHKCl.

Significance: F(3,12)-test 5 8.8843**; R2 5 0.7691**.

EUF and AL extraction of soil P and K 605

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CONCLUSIONS

Based on the statistically significant correlations among soil P and K

parameters determined by EUF and AL extraction, it was possible to

establish mathematical functions describing the comparability of themethods for the selected pseudogley soils from eastern Croatia. This

Table 5. The comparison of soil P2O5 data obtained by AL–extraction of

pseudogley soils and those predicted by regression function using EUF-P

fractions and soil PH (nutrient content expressed in mg kg21 dry soil)

Locality AL-P2O5 (measured) AL-P2O5

(regression)

Difference ¡ %

1 137.6 135.4 1.61

2 128.0 128.9 0.74

3 174.4 167.8 3.94

4 200.0 192.0 4.14

5 144.8 126.6 14.35

6 124.0 108.9 13.87

7 214.4 196.5 9.12

8 185.6 188.8 1.70

9 104.8 117.4 10.77

10 102.4 125.0 18.05

11 179.6 167.6 7.16

12 141.2 181.8 22.33

Mean 153.1 153.1 8.98

Figure 2. Correlation between EUF extracted potassium in the first EUF

fraction (EUF-K-I; mg kg21 of soil dry weight) and ammonium acetate–lactate–

extracted potassium (AL-K2O; mg kg21 of soil dry weight) from pseudogley soils

at 12 localities in eastern Croatia (data points represent means of five replicates).

606 T. Teklic et al.

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research confirmed the importance of soil pH for P extractability, as well

as clay content and selectivity for K. Further comprehensive research

regarding the comparison of EUF and AL methods in terms of P and K

availability in pseudogley soils is necessary, where plant nutrient

acquisition specificity and a great number of interrelated soil and climate

factors should be considered.

ACKNOWLEDGMENTS

The authors thank to the anonymous reviewers for their useful comments

and suggestions.

Table 6. Multiple regression analyses of the relationships among AL- and

EUF-extractable potassium (mg per 100 g dry soil) and selective mineral clay

content (SMC) in selected pseudogley soils of eastern Croatia. (** P ( 0.01)

Parameter Standard deviation Variability (%)

EUF-K 3.28 23.57

SMC (%) 2.83 16.76

EUF-K-Q 0.08 23.04

AL-K2O 3.72 17.90

Regression function: AL-K2O 5 14.6566 + 2.1822 6 EUF-K 23.736 6 SMC

+ 109.004 6 EUF-K-Q.

Significance: F(3,12)-test 5 31.7598**; R2 5 0.9225**.

Table 7. The comparison of soil K2O data obtained by AL-extraction of

pseudogley soils and those predicted by regression function using EUF-K

parameters and selective mineral clay content (nutrient content expressed in mg

kg21 dry soil)

Locality AL-K2O (measured) AL-K2O (regression) Difference ¡ %

1 210.0 189.1 9.95

2 195.2 200.0 2.44

3 219.6 217.4 1.00

4 183.2 173.6 5.25

5 243.6 241.8 0.75

6 210.0 222.4 5.92

7 294.0 290.9 1.06

8 137.2 154.6 12.69

9 184.0 173.8 5.55

10 203.6 204.2 0.28

11 205.2 208.0 1.35

12 206.8 213.0 3.00

Mean 207.70 207.39 4.10

EUF and AL extraction of soil P and K 607

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